1. Field of the Invention
The present invention relates to an ink container used in an inkjet recording device.
2. Description of the Related Art
Various methods of supplying ink to a recording head used in an inkjet recording device are known.
In particular, a small recording device, such as that for personal use, often has a structure in which ink is directly supplied to a head from an ink container which is removably mounted to the head.
In such an ink supplying method, a negative pressure controlling mechanism is provided at the ink container which directly supplies ink to the head.
The negative pressure to be controlled is set in equilibrium with the retentivity of a meniscus formed at the ink discharging unit of the head so as to be large enough to prevent ink from leaking from an ink discharging unit of the head, and also within a range which allows the recording head to discharge ink.
Hitherto, many negative pressure controlling mechanisms have generated a suitable negative pressure by the retentivity of ink obtained from an ink absorbent that is accommodated in an ink container. The ink absorbent comprises an aggregate of porous material or fibrous material including and holding the ink.
Recently, in order to achieve high-speed recording, pigment ink is used to increase ink capacity, the efficiency with which ink is contained, and the durability of a recording image.
Accordingly, a structure which directly stores the ink in the container without using an absorbent is becoming frequently used.
As a negative pressure controlling mechanism used in this structure, a movable member is used in a portion of an ink containing space and is biased with, for example, a spring in a direction in which the volume of the ink containing space is increased. In addition, a valve mechanism which opens when the negative pressure (which increases as the amount of ink is reduced in an ink containing unit) reaches a predetermined value is provided.
An example of a valve structure shields the ink containing space from outside air by the retentivity of an ink meniscus produced in a very small gap which is formed in an external wall of the ink container and which connects the ink containing space and the outside air.
In general, a valve structure is used in which outside air is introduced into the ink containing space by breaking the ink meniscus produced in this gap when the negative pressure in the ink containing space becomes equal to or greater than the meniscus retentivity due to the use of ink.
The value of the negative pressure in the ink containing space to which outside air is being introduced at this time can be controlled by the retentivity of the ink meniscus in the gap at the external wall and by the size of the gap.
According to U.S. Pat. No. 5,600,358, which is a first related example, as shown in FIG. 14, an opening connecting the inside of an ink container and the outside and a ball 24 mounted to the opening are provided.
U.S. Pat. No. 5,600,358 discloses a structure in which an orifice 20 for introducing outside air is formed by a gap formed by the ball 24 and the opening.
In U.S. Pat. No. 5,600,358, a narrow labyrinth 30 (air introducing path) connects an opening 18 where the ball is disposed and an opening 44 in contact with the outside air.
The labyrinth 30 prevents ink in the ink container from leaking to the outside when the force of an ink meniscus formed in the orifice is overcome (that is, a liquid seal is broken).
In addition, the labyrinth 30 restricts evaporation of the ink having its meniscus formed in the gap.
U.S. Pat. No. 6,168,267, which is a second related example, discloses, as shown in FIGS. 15 and 16, an ink cartridge comprising an ink containing unit 12, an air chamber 66, a ventilation opening 64 formed between the outside air and the air chamber 66, and a supply port 94 for guiding out the ink in the ink containing unit.
In U.S. Pat. No. 6,168,267, a pressure adjustor 98 and a bubble generator 40 are also provided.
The force of a meniscus in an orifice formed at an aperture 42 of the bubble generator 40 (which is formed at an external wall of the ink cartridge) maintains the outside pressure and the pressure in the ink containing unit at optimum values.
The force of the meniscus formed in the orifice prevents ink from flowing out of the cartridge from the ink containing unit 12 on the one hand, and guides the outside air into the ink containing unit 12 on the other.
The function of the bubble generator 40 in U.S. Pat. No. 6,168,267 corresponds to that of the labyrinth 30 in U.S. Pat. No. 5,600,358.
However, the structures disclosed in U.S. Pat. Nos. 5,600,358 and 6,168,267 have problems due to, for example, the acceleration that is produced when a carriage is subjected to main scanning, falling of the container, application of shock to the container, reduction in viscosity when the temperature of the ink increases, and a difference between the internal and external air pressures of the container.
When a liquid seal provided by the meniscus force is broken, ink cannot be held by a narrow labyrinth (air introducing path) alone, thereby causing the ink to flow out directly to the surrounding environment from the ink containing chamber 12.
In addition, when a channel is formed by hermetically sealing with a cover or a sealant an open side of a groove formed in the external wall of the ink container, the following problem occurs.
When the sealant does not properly seal the open side or when the sealant is damaged by the application of shock thereto, a flow path itself is exposed to the atmosphere, thereby breaking the liquid seal provided by the meniscus force.
As a result, the ink in the ink containing chamber directly leaks to the outside.